mail/exim: update 4.97 -> 4.97.1, fix CVE-2023-51766

• Bug: https://bugs.exim.org/show_bug.cgi?id=3063
• Announcement:

PR: 276075
Approved-by: fluffy (implicit)
Security: CVE-2023-51766
Changes: https://lists.exim.org/lurker/message/20231228.211920.dd3e6d22.en.html